The general evolution capacitive power ground planes began with patents granted to Sisler of Convergent Systems and to Howard (the author of this application) in U.S. Pat. Nos. 5,079,069; 5,155,655; 5,161,086. These structures utilized thin power and ground sandwiches to provide a distributed capacitive electrical charge to active devices, normally mounted on the surface of the PCB. These distributed planes replaced the need for bypass capacitors in smaller values, typically 0.1 μfd or less and smoothing electronic noise on the power ground planes to reduce radiated emissions from the printed circuit board which are harmful to the operation of other devices and are regulated by FCC regulation.
The greatest limitation to the successful operation of these distributed capacitive planes is the remaining noise that is radiated from the edge of the planes. Up to 95% of radiated emission from the power ground planes is radiated from the edge of the planes. The reason for this is that pulses of electronic noise travel across the planes on various patterns which may be detected at various points. When these electronic noise pulses reach the edge on the plane the impedance raises from the very low impedance, which is a result of the high capacitance thin dielectric of the layer and low inductance of the closely coupled conductive planes of the power ground sandwich, and rises to the very high impedance of the unterminated edge. This causes reflection of some of the energy and radiation of electronic noise of the remainder. The result of this is much the same as an antenna VSWR with the total energy being divided between radiated and reflected energy.
The use of capacitive layers such as 0.002″ FR4 dielectric which is a common dielectric used in the printed circuit industry at the time of this writing, actually make the problem worse than standard ground/power systems that are not closely coupled. The distributed capacitance plane better distributes the noise on the plane to all sectors of the printed circuit board, depending on design.
Improved materials, such as Cply from 3M have increased the dielectric constant of the dielectric material in the power ground sandwich. This has greatly improved the efficiency of the sandwich layer in reducing noise. Lower plane impedance and greater point source current capacity for less voltage sag mean less electronic noise is created to be resolved by the distributed capacitance plane. However even the improved materials do nothing to solve the termination problem of all edges and features of the printed circuit board power or ground conductive layers. As a result emissions continue, albeit at a lower general level.
Testing by industry sources has demonstrated that improved dielectric constant and reduced thickness of the capacitive layer has little beneficial effect in reducing edge emissions over standard 0.002″ Fr4 materials at very high frequencies, above 1 GHz.
For this reason it is a benefit to the printed circuit industry to find a cost effective solution to this problem that will reduce printed circuit board electronic noise edge emissions at high frequencies. The invention shown in this application will reduce edge emissions from conductive sources including planes, capacitive sandwiches composed of power and ground planes, and circuit conductors at virtually no increase in material or processing costs.